Maes Llwyn (SH 435 920)
There has been a Significant Height Revision to a hill that is listed in The Welsh P15s, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips.
LIDAR image of Maes Llwyn (SH 435 920) |
The Welsh
P15s – Welsh hills with 15m
minimum drop, irrespective of their height, with an accompanying sub list entitled the Welsh Sub-P15s,
with the criteria for this sub category being all Welsh hills with 14m or more
and below 15m of drop. The list is authored by Myrddyn Phillips, with the
Introduction to the list appearing on Mapping Mountains on the 10th
May 2019.
The Welsh P15s by Myrddyn Phillips |
When the listing that became known as The Welsh P15s was being compiled, this hill was listed with 25m of drop, based on the 77m summit spot height positioned on or near to a covered reservoir that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map and the 52m bwlch spot height that appears on the Ordnance Survey 1:50,000 Landranger map.
Extract from the Ordnance Survey 1:25,000 Explorer map |
LIDAR summit image of Maes Llwyn |
The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey or Harvey map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR, also included are hills whose summit map data is missing an uppermost ring contour when compared to the data produced by the Trimble or by LIDAR analysis.
Therefore, this hill’s new listed summit height is
74.0m and this was derived from LIDAR analysis, this is 3m lower than the
previous listed summit height of 77m which was based on the spot height positioned
on or near to a covered reservoir that appeared on the Ordnance Survey Vector
Map Local hosted on the Geograph website and which was entitled the Interactive
Coverage Map.
The full details for the hill are:
Group: Ynys Môn
Name: Maes Llwyn
OS 1:50,000 map: 114
Summit Height (New Height): 74.0m (LIDAR)
Summit Grid Reference: SH 43593 92022 (LIDAR)
Bwlch Height: 54.9m (LIDAR)
Bwlch Grid Reference: SH 43658 91747 (LIDAR)
Drop: 19.1m (LIDAR)
Myrddyn Phillips
(September 2021)
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